Hydrogen Activation and Metal Hydride Formation Trigger Cluster Formation from Supported Iridium Complexes

Lu, Jichang; Aydin, Ceren; Browning, Nigel D.; Gates, Bruce C.

doi:10.1021/ja211380p

Cited by 53 publications

(80 citation statements)

References 36 publications

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“…We recognize that, in previous work,25 samples similar to ours incorporating iridium complexes bonded to HY zeolite were characterized by an IR band at 2068 cm −1 (which we have attributed to a carbonyl band), and the authors suggested that it was evidence of an IrH vibration because they inferred that it “shifted” to 1509 cm −1 after an isotopic exchange with D 2 . However, the apparent shift does not match the frequencies calculated in the harmonic approximation,21 and we suggest that it was indeed a carbonyl band (which might have arisen from trace CO impurities).…”

Section: Resultsmentioning

confidence: 49%

Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Martínez-Macias

Chen

Dixon

et al. 2015

Chemistry A European J

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A family of HY zeolite-supported cationic organoiridium carbonyl complexes was formed by reaction of Ir(CO)2(acac) (acac = acetylacetonate) to form supported Ir(CO)2 complexes, which were treated at 298 K and 1 atm with flowing gas-phase reactants, including C2H4, H2, 12 CO, 13 CO, and D2O. Mass spectrometry was used to identify effluent gases, and infrared and X-ray absorption spectroscopies were used to characterize the supported species, with the results bolstered by DFT calculations. Because the support is crystalline and presents a nearly uniform array of bonding sites for the iridium species, these were characterized by a high degree of uniformity, which allowed a precise determination of the species involved in the replacement, for example, of one CO ligand of each Ir(CO)2 complex with ethylene. The supported species include the following: Ir(CO)2, Ir(CO)(C2H4)2, Ir(CO)(C2H4), Ir(CO)(C2H5), and (tentatively) Ir(CO)(H). The data determine a reaction network involving all of these species.

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Section: Resultsmentioning

confidence: 49%

Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Martínez-Macias

Chen

Dixon

et al. 2015

Chemistry A European J

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“…[4c] In contrast, the higher stability of the analogous iridium complexes demonstrated by our results (both experimental and computational) allows a resolution of the reaction network accounting for the corresponding conversions involving the iridium complexes, as shown in Scheme 1. [7,11] Thus, in Scheme 1 we propose the formation of Ir(C 2 H 5 )(H) as an intermediate after exposure of the sample to H 2 and before the adsorption of a dinitrogen ligand. [10] When the sample came in contact with H 2 at room temperature, an ethylene ligand on iridium was rapidly transformed to C 2 H 5 , with a hydride ligand presumably formed on the Ir atom, and with C 2 H 4 being displaced.…”

Section: Discussionmentioning

confidence: 99%

“…[10] When the sample came in contact with H 2 at room temperature, an ethylene ligand on iridium was rapidly transformed to C 2 H 5 , with a hydride ligand presumably formed on the Ir atom, and with C 2 H 4 being displaced. [7,11] Thus, in Scheme 1 we propose the formation of Ir(C 2 H 5 )(H) as an intermediate after exposure of the sample to H 2 and before the adsorption of a dinitrogen ligand.…”

Section: Discussionmentioning

confidence: 99%

Mononuclear Iridium Dinitrogen Complexes Bonded to Zeolite HY

Yang

Chen

Martínez-Macias

et al. 2014

Chemistry A European J

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The adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N2 . Four supported species formed in various flowing gases: Ir(N2 ), Ir(N2 )(N2 ), Ir(C2 H5 )(N2 ), and Ir(H)(N2 ). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2 , Ir(N2 ) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N2 ) formed transiently in flowing CO, and in the presence of H2 , rather stable iridium hydride complexes formed. Four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.

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“…The process typically involves reduction, migration of metal species on the support surface, and metal-metal bond formation processes, as demonstrated particularly by Gates and coworkers (154).…”

Section: (B) Models Involving Transition Metals Other Than Ironmentioning

confidence: 99%

“…In this regard, the hydrogen spillover concept employed by Gates and coworkers to explain their results (154), is terra incognita for DHC purposes still full of controversies, especially for the transfer of hydrogen species onto the non reducible support surfaces (155). Our ongoing work on spillover of hydrogen based on combined Pd/SiO 2 clusters (Pd 4 tetrahedral cluster located on top of the cyclic silica consisting of three SiO 4 -linkages) indicates the main role of the H 2 -catalyst (the transporter of the spillover-hydrogen species), and the adsorbed (capped on palladium vertexes) hydrogen molecules (151).…”

Section: (B) Models Involving Transition Metals Other Than Ironmentioning

confidence: 99%

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

Asatryan

Ruckenstein

2014

Catalysis Reviews

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Molecular hydrogen is the simplest and most abundant compound in the universe and is involved in numerous industrial chemical processes. In conventional chemistry, dihydrogen typically plays the role of a reductant and a reagent for homogeneous and heterogeneous hydrogenation processes such as the industrial and enzymatic ammonia formation, reduction of metallic ores and hydrogenation of unsaturated fats and oils. However, there are also processes in which molecular hydrogen participates as promoter, and even as catalyst. The catalytic role of the dihydrogen in free-valence migration in irradiated polymers and the interstellar isomerization of the formyl cation (protonated carbon monoxide) are well-documented examples of such processes. Recently, this issue has received new attention. Dihydrogen has been shown to play the role of a dehydrogenation catalyst (involving particularly metallocomplexes and inorganic materials), a relay (pass-on) transfer molecular agent and a transporter of protons.This review article, combined with original results, is focused on the mechanisms of the chemical processes where dihydrogen demonstrates catalytic behavior. We will call these processes (with somewhat broader meaning of the term) "dihydrogen catalysis" (DHC) which also includes the reactions mediated by transition metal dihydrides. Dihydrides are tentatively considered as pre-activated dihydrogen, coordinated to a metal center or implanted into a solid surface/support. DHC reactions are classified into five major reaction types: (i) dihydrogen-assisted relay transport of H-atoms (H2-RT); (ii) dihydrogen-assisted stepwise relay transport of H-atoms or of a free valence (sH2-RT); (iii) dihydrogen-assisted proton transport (H2-PT); (iv) dihydrogen-assisted dehydrogenation (H2-DeH); and (v) pre-activated dehydrogenation (PA-DeH). The classification of these mechanisms is Color versions of one or more of the figures in the article can be found online at www. tandfonline.com/lctr. 403 Downloaded by [George Mason University] at 02:43 28 September 2014 R. Asatryan and E. Ruckensteinbased on a detailed analysis of numerous potential energy surfaces studied by DFT and ab initio methods in conjunction with available experimental data. The H2-RT, H2-DeH, and PA-DeH processes occur via cyclic transition states. The relay H2-RT transport involves the H-H-H triad linked to both H-donor and H-acceptor centers, whereas the transition state ring in the H2-DeH dehydrogenation processes involves a H-H-H-H tetrad with the dihydrogen catalyst located in the middle. The H2-PT mechanism provides the transport of a proton mediated by dihydrogen combined in a triangular (H 3 + )-carrier unit. There are also practically important processes stimulated by dihydrogen such as the hydrogen spillover and hydrogen build-up in electronics, in which the catalytic role of dihydrogen is ambiguous, either because of the uncertainties in mechanisms, or prevailing traditional views. Some examples are briefly discussed in the framework of the concept of dihydrogen ...

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Hydrogen Activation and Metal Hydride Formation Trigger Cluster Formation from Supported Iridium Complexes

Cited by 53 publications

References 36 publications

Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Mononuclear Iridium Dinitrogen Complexes Bonded to Zeolite HY

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

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